I have a Google Apps for your domain account that I have used for several years. I originally set up this account with a very generic username as a spam protection measure since I knew I could setup additional nicknames for the account and send from those instead. I figured that if I ever started getting a ton of spam at my primary account, this would make it easier to just block messages sent to the current account and switch to another nickname.
When I first got my iPhone 3GS, push Gmail was not an option for me since only one exchange (push gmail uses this protocol) account was allowed, and I needed to connect to the exchange server at the office for my work email and calendar. With this limitation, I set up my Google Apps Gmail account through IMAP. This allowed me to log in with the basic username like I have to when going to the web interface, but still allowed me to setup the email account on the phone to send as the primary nickname I use for that account.
Now that iOS4 allows multiple exchange accounts, I am able to set up push Gmail. However, even though I can enter the account information just like I did with the IMAP setup and save It initially, the email account automatically gets changed back to the basic username after I try to load the mailbox for the first time. Therefore, no matter which nickname the message was sent to, any messages I send show that they are sent from this basic account (which I truthfully don't want people to see at all for the spam protection reason above if I could have the choice).
Is there a way to setup push Gmail using the nickname that I want to on the iPhone? If not, is the problem an iOS problem, and Exchange/ActiveSync problem, or a push Gmail limitation?